1. Field of the Invention
The present invention relates to heat resistant phosphate compounds, sintered bodies thereof and a manufacturing process of such sintered bodies. More particularly, the present invention relates to heat resistant phosphate compounds having very excellent low-expansibility and thermal shock resistance, sintered bodies of such a phosphate compound, and a process for manufacturing such sintered bodies.
2. Description of the Prior Art
In recent years, a demand for materials excellent in heat resistance and low thermal expansion properties has been increasing with the progress of industrial technology. Under such a demand, it has been recognized that zirconyl phosphate [(ZrO).sub.2 P.sub.2 O.sub.7 ] is promising as an excellent heat resistant and low expansion material.
Further, alkaline earth metal phosphate compounds with a specific composition have been proposed as low expansion compounds (Communications of the American Ceramic Society 70 [10] C-232 C-236 (1987) and the specification of U.S. Pat. No. 4,801,566).
However, it has been pointed out that phosphate compounds such as zirconyl phosphate or the like, although having an excellent low expansion property, are pyrolyzed at a high temperature of 1,200.degree. C. or more and phosphorus (P) evaporates. For example, there is a problem that after exposure to heat at 1,400.degree. C. for 100 hours, zirconyl phosphate exhibits an ignition loss of 19% and sodium zirconium phosphate exhibits that of not less than 36%.